Gas turbine engines are continually being driven to provide higher thrust efficiencies to maximize performance. As hot engine gases flow around airfoils in the turbine section, turbulent flow can be generated along an external surface of the airfoils, which adversely affects efficiencies. One proven method to improve efficiency includes optimizing airfoil/endwall shapes and minimizing turbine cooling air usage to reduce friction and pressure drag around the airfoil.
Airfoil friction drag is created by a combination of friction loss and mixing loss. Friction loss from near-wall turbulence that impacts a boundary layer along the external surface of the airfoil can result in a significant energy loss. In a cooled airfoil configuration, film cooling air may be targeted towards different areas or via different shaped holes to lessen the impact on friction and mixing loss factors. In an uncooled airfoil configuration, such features are not available making it difficult to improve efficiency.